My apologies, I was merely confirming what I thought (and still think?) another poster had stated.
But that is not clear.
Would you conceed there is a difference between sustaining a spell, and extending it?
The only spells that need to be sustained are those of duration Concentration.
And should you wish to extend the duration of a spell, you should refer to MuVi, as you are changing a parameter of said spell, exactly as per Wizard's Reach, save only that you are affecting duration rather than range.
On this we agree fully.